It is well known to provide mechanical components, such as those found in gas turbine engines, with cooling circuits or systems in order to permit operation of machinery containing those components at temperatures higher than would be possible without such cooling systems. The higher operating temperatures permitted by such cooling systems result in improved performance and efficiency without damage to the cooled components.
In order to realize such improved performance and efficiency, gas turbine engines have cooling circuits associated with selected critical components in the engine. Examples of cooling circuits in a gas turbine engine include a series of cooling passages inside critical components, such as turbine blades, vanes, and shrouds. During the operation of the engine, a cooling fluid is passed through these passages to enable the components to withstand temperatures which would otherwise damage or destroy them.
The first prototype of a gas turbine engine design sometimes fails because of a design or manufacturing defect in the cooling circuits associated with critical cooled components. To minimize the likelihood of such an occurrence, it would be desirable to measure the thermal performance of the cooling circuits in those critical components as soon as the first of those components is made. The results of this measurement would be used to determine whether or not the actual thermal performance of the cooling circuit agrees closely with predicted performance and whether or not a cooling circuit design meets the cooling requirements of the component in which it is to be used.
At the present time, these measurements are not obtained because no practical way of obtaining them is known. Consequently, the first prototype of an engine design is always operated with no prior measurements of the actual thermal performance of the cooling circuits.
In addition to a need for measuring the thermal performance of cooling circuits as described above, there is also a need to exercise process control in the manufacture of critical cooled components once a cooling circuit design has been decided upon. Specifically, there is a need to verify that each cooled component and its cooling circuit has the required thermal performance. This could be accomplished by measuring the actual or as-built thermal performance of each component and its cooling circuit. As in the case of comparing the actual performance of the cooling circuits against design predictions, there is no practical way of doing this at the present time.
In addition to providing cooling passages in selected components, other components in gas turbine engines have passages through which heating fluid is passed to selectively heat those components. For example, selected portions of a gas turbine engine may be heated to control thermal expansion of those portions of the engine. This would be desirable in a situation such as a system for controlling the clearance between the tips of the blades in the compressor or turbine and the casing surrounding the blades. It would also be desirable in a situation where it was necessary to maintain the temperature of two parts of the engine the same to avoid thermal stresses and the like.
In the past, no effort was made to measure the actual or as-built thermal performance of cooling or heating circuits until a prototype engine was built, instrumented, and operated. There are at least two significant drawbacks in relying only on such engine tests to confirm as-built thermal performance. One, failure of the heating or cooling circuits to satisfy their design intent can and sometimes does result in damaging or destroying the engine in which they are operated. Two, the length of the design cycle from initial design of the heating or cooling circuits to actual verification of the adequacy of their performance can be many years.
Consequently, a need exists for a test which will permit the thermal performance of the heating or cooling circuit of an engine component to be measured as soon as the first component is actually fabricated, before it is installed and operated in an engine. This may be accomplished in accordance with the invention of this application by measuring the temperature distribution on a preselected surface of the component when the component is exposed to cooling fluid flow having predetermined characteristics, such as one or more of a predetermined flow rate, pressure, and temperature.